Because the soluble extract from the nephritogenic protoplasmic membrane has been a heterogeneous material, purification procedures have been pursued. One approach that has been successful has been the use of immunologic precipitation of the cross-reactive component from the extract with the cross-reactive antibody and chromatographic column separation of the dissociated precipitate. Unfortunately, while the method is a reliable one it is not useful inasmuch as the major part of the cross-reactive antibody is denatured either during dissociation and/or elution from the column. An alternative approach of coupling the antibody-rich gamma-globulin to BAC and employing the conjugate as an immunoadsorbent column too has been disappointing. While coupling and adsorption appears to have occurred the eluation of the material from the column has presented difficulties. If a solution of the extract has its pH adjusted to 10.0 a precipitate forms which upon removal leaves a supernatant which still contains cross-reactive properties and which now behaves differently on G-25. Two peaks can now be obtained, only one which contains the activity and which upon recycling through the same column now yields three peaks only one of which contains the activity. Thus, it would appear that further purification of the cross-reactive component present within the extract from the streptococcal protoplasmic membrane has been accomplished.